When is a tablet a PC? When it’s running Windows 8. Conversely, when is a tablet not a PC? When it bears the Apple logo. In a second quarter littered with negative sales figures, it took some fancy footwork to lump Apple Mac shipments in with an industry decline that’s lasted five quarters.

In its estimates of PCs shipped during the last quarter, Gartner earlier this week announced PC shipments on average fell 10.9 percent. Even Apple – which has consistently beaten PC numbers – fell 4.3 percent. However, in a curious note, the firm explained the figures included desktops, mobile PCs and mini-notebooks – but not iPads. What gives?…

Because the desktop and mini-notebook markets are being obliterated by tablets, that’s why – and according to Gartner’s own June 2013 tablet shipment estimates.

Gartner’s July 2013 PC shipment estimates, released earlier in the week, help complete the picture. According to data, falling demand for PCs in the United States was led by a 15.7 percent drop by Toshiba, with Hewlett-Packard not even able to tread water.

Here, this is how Gartner explained the situation:

We are seeing the PC market reduction directly tied to the shrinking installed base of PCs, as inexpensive tablets displace the low-end machines used primarily for consumption in mature and developed markets.

As for mini notebooks, that market is collapsing, the firm added.

Quick, which company sells the No. 1 and No. 2 best-selling tablets (hint: not Microsoft)

Because Apple uses the iOS software to power its iPads and OS X for its Macs, discounting iPad shipments has removed a large portion of Apple’s units shipped.

Chart via Fortune.

And as Gartner considers Windows 8 a desktop operating system, it has added the tiny sales of Windows 8 slates to all Windows 8 desktop and notebook PCs.

While Windows 8 has been blamed by some as the reason for the PC market’s decline, we believe this is unfounded as it does not explain the sustained decline in PC shipments, nor does it explain Apple’s market performance.